No abstract

Two novel phloroglucinol–terpenoid adducts (1 and 2), featuring a rare 2,2,4-trimethyl-cinnamyl-β-triketone unit, were isolated from the buds of Cleistocalyx operculatus. Their structures with absolute configurations were established by spectroscopic analyses, single-crystal X-ray diffraction, and quantum chemical calculations. Structurally, compound 1 represents a new carbon skeleton possessing a densely functionalized tricyclo­[11.3.1.03;8]­heptadecane bridged ring system with an unusual bridgehead enol. Compounds 1 and 2 exhibited significant in vitro antiviral activities against respiratory syncytial virus (RSV).

Four novel phloroglucinol derivatives (1-4) featuring a 2,4-dimethyl-cinnamyl-phloroglucinol moiety, along with their putative biosynthetic precursors 5 and 6, were isolated from the leaves of Cleistocalyx operculatus. Compounds 1 and 2 are two pairs of new enantiomeric phloroglucinol dimers possessing an unprecedented polycyclic skeleton with a highly functionalized dihydropyrano[3,2- d]xanthene tetracyclic core. Compounds 3 and 4 are two new phloroglucinol-terpene adducts (PTAs) with a novel carbon skeleton. The structures of 1-4 including their absolute configurations were unambiguously accomplished by combination of extensive spectroscopic analyses, X-ray crystallography, and quantum chemical ECD calculations. A hypothetical biosynthetic pathway for 1-4 was also proposed. Compound 1 exhibited a promising in vitro antiherpes simplex virus type-1 (HSV-1) effect.